Lift embedded structure out of eviction-related KubeletConfiguration fields

- Changes the following KubeletConfiguration fields from `string` to
`map[string]string`:
  - `EvictionHard`
  - `EvictionSoft`
  - `EvictionSoftGracePeriod`
  - `EvictionMinimumReclaim`
- Adds flag parsing shims to maintain Kubelet's public flags API, while
enabling structured input in the file API.
- Also removes `kubeletconfig.ConfigurationMap`, which was an ad-hoc flag
parsing shim living in the kubeletconfig API group, and replaces it
with the `MapStringString` shim introduced in this PR. Flag parsing
shims belong in a common place, not in the kubeletconfig API.
I manually audited these to ensure that this wouldn't cause errors
parsing the command line for syntax that would have previously been
error free (`kubeletconfig.ConfigurationMap` was unique in that it
allowed keys to be provided on the CLI without values. I believe this was
done in `flags.ConfigurationMap` to facilitate the `--node-labels` flag,
which rightfully accepts value-free keys, and that this shim was then
just copied to `kubeletconfig`). Fortunately, the affected fields
(`ExperimentalQOSReserved`, `SystemReserved`, and `KubeReserved`) expect
non-empty strings in the values of the map, and as a result passing the
empty string is already an error. Thus requiring keys shouldn't break
anyone's scripts.
- Updates code and tests accordingly.

Regarding eviction operators, directionality is already implicit in the
signal type (for a given signal, the decision to evict will be made when
crossing the threshold from either above or below, never both). There is
no need to expose an operator, such as `<`, in the API. By changing
`EvictionHard` and `EvictionSoft` to `map[string]string`, this PR
simplifies the experience of working with these fields via the
`KubeletConfiguration` type. Again, flags stay the same.

Other things:
- There is another flag parsing shim, `flags.ConfigurationMap`, from the
shared flag utility. The `NodeLabels` field still uses
`flags.ConfigurationMap`. This PR moves the allocation of the
`map[string]string` for the `NodeLabels` field from
`AddKubeletConfigFlags` to the defaulter for the external
`KubeletConfiguration` type. Flags are layered on top of an internal
object that has undergone conversion from a defaulted external object,
which means that previously the mere registration of flags would have
overwritten any previously-defined defaults for `NodeLabels` (fortunately
there were none).

pkg/kubelet/cm/cgroup_manager_test.go

@@ -23,52 +23,49 @@ import (
 	"testing"
 
 	"k8s.io/api/core/v1"
-	"k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig"
 )
 
 func Test(t *testing.T) {
 	tests := []struct {
-		input    string
+		input    map[string]string
 		expected *map[v1.ResourceName]int64
 	}{
 		{
-			input:    "memory",
+			input:    map[string]string{"memory": ""},
 			expected: nil,
 		},
 		{
-			input:    "memory=a",
+			input:    map[string]string{"memory": "a"},
 			expected: nil,
 		},
 		{
-			input:    "memory=a%",
+			input:    map[string]string{"memory": "a%"},
 			expected: nil,
 		},
 		{
-			input:    "memory=200%",
+			input:    map[string]string{"memory": "200%"},
 			expected: nil,
 		},
 		{
-			input: "memory=0%",
+			input: map[string]string{"memory": "0%"},
 			expected: &map[v1.ResourceName]int64{
 				v1.ResourceMemory: 0,
 			},
 		},
 		{
-			input: "memory=100%",
+			input: map[string]string{"memory": "100%"},
 			expected: &map[v1.ResourceName]int64{
 				v1.ResourceMemory: 100,
 			},
 		},
 		{
 			// need to change this when CPU is added as a supported resource
-			input:    "memory=100%,cpu=50%",
+			input:    map[string]string{"memory": "100%", "cpu": "50%"},
 			expected: nil,
 		},
 	}
 	for _, test := range tests {
-		m := kubeletconfig.ConfigurationMap{}
-		m.Set(test.input)
-		actual, err := ParseQOSReserved(m)
+		actual, err := ParseQOSReserved(test.input)
 		if actual != nil && test.expected == nil {
 			t.Errorf("Unexpected success, input: %v, expected: %v, actual: %v, err: %v", test.input, test.expected, actual, err)
 		}